High-pressure discharge lamps that can provide a large amount of light are mainly used for light source devices used in optical apparatuses such as liquid crystal projectors and exposure apparatuses. Such a high-pressure discharge lamp includes: a light-emitting portion having a space in which a light-emitting material or a halogen-cycle product, such as mercury and a halogenated product, is enclosed; and a pair of main electrodes arranged in the light-emitting portion so as to be opposed to each other. At the time of start of lighting, a high voltage is applied, discharge is caused by dielectric breakdown between the main electrodes, and thereby the light-emitting material is excited to emit light.
In recent years, in order to cause a high-pressure discharge lamp to function as a point light source on the one hand and to enhance the light-emitting efficiency on the other hand, the amount of a light-emitting material enclosed has been increased, while the volume of the internal space of the light-emitting portion has been reduced. Accordingly, the internal pressure of the light-emitting portion during lighting becomes significantly high. The internal pressure in some recent examples is reported to be around 200 atm or more. Furthermore, in the above type of optical apparatuses, it is demanded to reduce time taken for relighting (hot start), as well as time taken for initial lighting (cold start).
Generally, the higher the internal pressure of a light-emitting portion is, the higher the voltage required to start discharge is. Therefore, in order to relight a high-pressure discharge lamp while the internal temperature of its light-emitting portion is high (hot start), it is necessary not only to apply a high voltage but also to wait until the temperature of the high-pressure discharge lamp is decreased to a certain degree. In addition, a high voltage (e.g., 10 kV or more) needs to be applied even for initial lighting (cold start).
However, applying a high voltage to start lighting of a high-pressure discharge lamp is accompanied with some problems. For example, dielectric breakdown may occur not only between the main electrodes but also in unintended parts (e.g., dielectric breakdown of a dielectric cable coating, and creeping discharge in a connector or a connection terminal), leading to electric shock, or an electric circuit provided in the optical apparatus may be erroneously operated by noise at the time of application of a high voltage.
In response, techniques for starting lighting of a high-pressure discharge lamp by a lower voltage have been developed (see Patent Literature 1, for example). As shown in FIG. 5, a light source device 1 of Patent Literature 1 is composed of a high-pressure discharge lamp 2, an auxiliary lamp 3 formed separately from the high-pressure discharge lamp 2, a reflector 4, and a base B.
The high-pressure discharge lamp 2 is composed of a light emitting tube 5 which includes a light-emitting portion 5a having an internal space in which a light-emitting material M1 such as mercury is enclosed, and sealing portions 5b which seal the internal space of the light-emitting portion 5a; and power feeding means 6 which includes: a pair of main electrodes 6a arranged in the light-emitting portion 5a so as to be opposed to each other; a pair of metal foils 6b electrically connected to the main electrodes 6a, respectively, and embedded in the sealing portions 5b, respectively; and a pair of external lead rods 6c, one ends of which are electrically connected to the metal foils 6b, respectively, and embedded in the sealing portions 5b, respectively, and the other ends of which project outward from the light emitting tube 5.
The auxiliary lamp 3 is composed of a cylindrical discharge container 7 having a discharge space 7a in which a material that generates ultraviolet rays UV1 and UV 2 when excited by discharge is enclosed as a discharging medium M2; and a pair of external electrodes 9a, 9b wound around the respective outer peripheral surfaces of both end portions of the discharge container 7.
The reflector 4 is composed of a main body portion 4a on which a concave reflection surface 4c is formed, and a sealing portion attachment portion 4b projecting rearward from the bottom portion of the main body portion 4a. A first insertion hole X, in which one of the sealing portions 5b of the high pressure discharge lamp 2 is inserted, is formed from the sealing portion attachment portion 4b to the bottom portion 4d. In addition, a second insertion hole Y, in which the same sealing portion 5b is inserted and fixed with an adhesive, is formed in the base B. Furthermore, a recess Z is formed on the base B, and thus a space A is created between the bottom portion of the reflector 4 and the inner surface of the recess Z when the base B is attached over the bottom portion of the reflector 4 from the outside.
The light source device 1 is produced in the following steps one of the sealing portions 5b of the high-pressure discharge lamp 2 is inserted into the first insertion hole X of the reflector 4; the discharge container 7 of the auxiliary lamp 3 is then provided near the peripheral surface of the sealing portion 5b projecting from the first insertion hole X along the direction perpendicular to the longitudinal direction of the seating portion 5b; the sealing portion 5b is subsequently inserted into the second insertion hole Y and the base B is attached over the bottom portion of the reflector 4; and the second insertion hole Y is filled with an adhesive to finally fix the high-pressure discharge lamp 2 to the base B. The reason why the auxiliary lamp 3 has to be provided as described above along the direction perpendicular to the longitudinal direction of the sealing portion 5b is that since the entire length of the light source device 1 is defined and the auxiliary lamp 3 needs to have a certain length, the auxiliary lamp 3 cannot be fully accommodated in the recess Z even if it is attempted to locate the auxiliary lamp 3 along the sealing portion 5b. 
When starting lighting of the high-pressure discharge lamp 2 having the above structure, a high-frequency voltage is applied between the external electrodes 9a, 9b of the auxiliary lamp 3. Thus, discharge is caused between the external electrodes 9a, 9b via the discharge space 7a of the discharge container 7, and the discharging medium M2 in the discharge space 7a is excited by the discharge and generates ultraviolet rays. The ultraviolet rays pass through routes UV1 and UV2 and then reach the light-emitting portion 5a. 
The ultraviolet rays having passed through the routes UV1 and UV2 strike the main electrodes 6a in the light-emitting portion 5a of the high-pressure discharge lamp 2, thereby promoting the discharge between the main electrodes 6a. 